In dewatering small coal or slack the deposit which settles on the dewatering screen offers considerable resistance to the passage of water. Also, the dewatering process becomes increasingly slower and more difficult with increasingly finer grain sizes of the processed material.
One method which had been used to increase the amount of liquid abstracted from fines comprised a revolving screen having steps located in one or several lateral planes or radial planes. The steps were to cause a loosening or rearrangement of the layers of material being dewatered as it moved to the discharge end and thereby reduce the resistance against dewatering. Initial concepts of this kind were, for example, disclosed in German Patent No. 378,453. Similar concepts were disclosed also in German Patent Nos. 945,317 and 1,157,551.
Notwithstanding the fact that the concept of stepping the revolving screen in non-vibratory centrifuges was well recognized, centrifuges incorporating the concept failed to achieve practical acceptance, and in German Patent No. 1,782,196 (representing an addition to German Patent No. 1,157,551) it was suggested that stepping should be specifically omitted in order to reduce the wear of the revolving screen. Accordingly, those skilled in the art have rejected the concept of stepping the revolving screens vibratory centrifuges as being impractical or non-beneficial in that the sought after improvements in liquid abstraction did not come about. Vibratory centrifuges having stepped revolving screens are apparently no longer used or offered for sale.
An object of the present invention is to provide a form of vibratory centrifuge having stepped revolving screens which ensure better liquid abstraction than can be obtained with vibratory centrifuges known in the prior art.